1CHRONYD(8)                   System Administration                  CHRONYD(8)
2
3
4

NAME

6       chronyd - chrony daemon
7

SYNOPSIS

9       chronyd [OPTION]... [DIRECTIVE]...
10

DESCRIPTION

12       chronyd is a daemon for synchronisation of the system clock. It can
13       synchronise the clock with NTP servers, reference clocks (e.g. a GPS
14       receiver), and manual input using wristwatch and keyboard via chronyc.
15       It can also operate as an NTPv4 (RFC 5905) server and peer to provide a
16       time service to other computers in the network.
17
18       If no configuration directives are specified on the command line,
19       chronyd will read them from a configuration file. The compiled-in
20       default location of the file is /etc/chrony.conf.
21
22       Informational messages, warnings, and errors will be logged to syslog.
23

OPTIONS

25       -4
26           With this option hostnames will be resolved only to IPv4 addresses
27           and only IPv4 sockets will be created.
28
29       -6
30           With this option hostnames will be resolved only to IPv6 addresses
31           and only IPv6 sockets will be created.
32
33       -f file
34           This option can be used to specify an alternate location for the
35           configuration file. The compiled-in default value is
36           /etc/chrony.conf.
37
38       -n
39           When run in this mode, the program will not detach itself from the
40           terminal.
41
42       -d
43           When run in this mode, the program will not detach itself from the
44           terminal, and all messages will be written to the terminal instead
45           of syslog. If chronyd was compiled with enabled support for
46           debugging, this option can be used twice to enable debug messages.
47
48       -l file
49           This option enables writing of log messages to a file instead of
50           syslog or the terminal.
51
52       -L level
53           This option specifies the minimum severity level of messages to be
54           written to the log file, syslog, or terminal. The following levels
55           can be specified: 0 (informational), 1 (warning), 2 (non-fatal
56           error), and 3 (fatal error). The default value is 0.
57
58       -p
59           When run in this mode, chronyd will print the configuration and
60           exit. It will not detach from the terminal. This option can be used
61           to verify the syntax of the configuration and get the whole
62           configuration, even if it is split into multiple files and read by
63           the include or confdir directive.
64
65       -q
66           When run in this mode, chronyd will set the system clock once and
67           exit. It will not detach from the terminal.
68
69       -Q
70           This option is similar to the -q option, except it only prints the
71           offset without making any corrections of the clock and it allows
72           chronyd to be started without root privileges.
73
74       -r
75           This option will try to reload and then delete files containing
76           sample histories for each of the servers and reference clocks being
77           used. The files are expected to be in the directory specified by
78           the dumpdir directive in the configuration file. This option is
79           useful if you want to stop and restart chronyd briefly for any
80           reason, e.g. to install a new version. However, it should be used
81           only on systems where the kernel can maintain clock compensation
82           whilst not under chronyd’s control (i.e. Linux, FreeBSD, NetBSD,
83           Solaris, and macOS 10.13 or later).
84
85       -R
86           When this option is used, the initstepslew directive and the
87           makestep directive used with a positive limit will be ignored. This
88           option is useful when restarting chronyd and can be used in
89           conjunction with the -r option.
90
91       -s
92           This option will set the system clock from the computer’s real-time
93           clock (RTC) or to the last modification time of the file specified
94           by the driftfile directive. Real-time clocks are supported only on
95           Linux.
96
97           If used in conjunction with the -r flag, chronyd will attempt to
98           preserve the old samples after setting the system clock from the
99           RTC. This can be used to allow chronyd to perform long term
100           averaging of the gain or loss rate across system reboots, and is
101           useful for systems with intermittent access to network that are
102           shut down when not in use. For this to work well, it relies on
103           chronyd having been able to determine accurate statistics for the
104           difference between the RTC and system clock last time the computer
105           was on.
106
107           If the last modification time of the drift file is later than both
108           the current time and the RTC time, the system time will be set to
109           it to restore the time when chronyd was previously stopped. This is
110           useful on computers that have no RTC or the RTC is broken (e.g. it
111           has no battery).
112
113       -t timeout
114           This option sets a timeout (in seconds) after which chronyd will
115           exit. If the clock is not synchronised, it will exit with a
116           non-zero status. This is useful with the -q or -Q option to shorten
117           the maximum time waiting for measurements, or with the -r option to
118           limit the time when chronyd is running, but still allow it to
119           adjust the frequency of the system clock.
120
121       -u user
122           This option sets the name of the system user to which chronyd will
123           switch after start in order to drop root privileges. It overrides
124           the user directive. The compiled-in default value is chrony.
125
126           On Linux, chronyd needs to be compiled with support for the libcap
127           library. On macOS, FreeBSD, NetBSD and Solaris chronyd forks into
128           two processes. The child process retains root privileges, but can
129           only perform a very limited range of privileged system calls on
130           behalf of the parent.
131
132       -U
133           This option disables a check for root privileges to allow chronyd
134           to be started under a non-root user, assuming the process will have
135           all capabilities (e.g. provided by the service manager) and access
136           to all files, directories, and devices, needed to operate correctly
137           in the specified configuration. Note that different capabilities
138           might be needed with different configurations and different Linux
139           kernel versions. Starting chronyd under a non-root user is not
140           recommended when the configuration is not known, or at least
141           limited to specific directives.
142
143       -F level
144           This option configures a system call filter when chronyd is
145           compiled with support for the Linux secure computing (seccomp)
146           facility. In level 1 the process is killed when a forbidden system
147           call is made, in level -1 the SIGSYS signal is thrown instead and
148           in level 0 the filter is disabled. The default value is 0.
149
150           It is recommended to enable the filter only when it is known to
151           work on the version of the system where chrony is installed as the
152           filter needs to allow also system calls made from libraries that
153           chronyd is using (e.g. libc) and different versions or
154           implementations of the libraries might make different system calls.
155           If the filter is missing some system call, chronyd could be killed
156           even in normal operation.
157
158       -P priority
159           On Linux, this option will select the SCHED_FIFO real-time
160           scheduler at the specified priority (which must be between 0 and
161           100). On macOS, this option must have either a value of 0 to
162           disable the thread time constraint policy or 1 for the policy to be
163           enabled. Other systems do not support this option. The default
164           value is 0.
165
166       -m
167           This option will lock chronyd into RAM so that it will never be
168           paged out. This mode is only supported on Linux.
169
170       -x
171           This option disables the control of the system clock. chronyd will
172           not try to make any adjustments of the clock. It will assume the
173           clock is free running and still track its offset and frequency
174           relative to the estimated true time. This option allows chronyd to
175           be started without the capability to adjust or set the system clock
176           (e.g. in some containers) to operate as an NTP server.
177
178       -v, --version
179           With this option chronyd will print version number to the terminal
180           and exit.
181
182       -h, --help
183           With this option chronyd will print a help message to the terminal
184           and exit.
185

FILES

187       /etc/chrony.conf
188

SEE ALSO

190       chronyc(1), chrony.conf(5)
191

BUGS

193       For instructions on how to report bugs, please visit
194       https://chrony.tuxfamily.org/.
195

AUTHORS

197       chrony was written by Richard Curnow, Miroslav Lichvar, and others.
198
199
200
201chrony 4.0                        2020-10-07                        CHRONYD(8)
Impressum